This is a national stage application under 35 U.S.C. xc2xa7371 of application Ser. No. PCT/EP99/04303, filed in Germany under the Patent Cooperation Treaty, and having an International Priority Date of Jun. 22, 1999.
The invention relates to a dual pump unit for connecting two hydraulic pumps. The hydraulic pumps operate either as so-called tandem pumps with the same volumetric delivery or as so-called contact pumps with different volumetric deliveries.
A dual pump unit is known from DE 195 36 997 C1, in which two axially disposed drive shafts of two hydraulic pumps are non-positively coupled together by means of a coupling piece. High-pressure lines and low-pressure lines are formed in a connecting piece surrounding the coupling piece in order to supply the cylinders of the hydraulic pumps cyclically with the high pressure and the low pressure via a respective control body. This publication also discloses the integration of a booster pump into the connecting piece in order to obtain a higher degree of pre-compression in the low-pressure line.
Connections between hydraulic pumps of different designs can be found, for example, in DE 32 38 362 A1, DE 42 25 380 A1 and DE 37 16 374 C2.
A disadvantage of the known dual pump units lies in the fact that the connecting member between the two hydraulic pumps is of a rigid structure and cannot be flexibly adapted to different conditions. Thus in practice there is on the one hand, for example, the need to connect two hydraulic pumps together by a simply formed connecting piece as inexpensively as possible, whereas, for example, other dual pump units require the integration of a booster pump, for example in the form of a gear pump, into the connecting piece without this greatly increasing the expenditure in construction terms. It has therefore been necessary until now for the intermediate pieces to be of a different basic construction for these different purposes, without being able to resort to common construction elements.
The object of the invention is therefore to provide a dual pump unit which, starting out from a basic construction, can easily be adapted to different configurations.
In this respect the invention is based on the recognition that the same basic elements can be returned to for all configurations as a result of dividing the connecting piece into two connection plates, each constructed in the same way for all configurations, and into an intermediate element which is disposed between the connection plates, is interchangeable and can be configured individually. Here the connection plates each comprise a recess in which the respective intermediate element can be at least partly inserted, so that the connection plates at least partly encompass the intermediate element radially and the intermediate element is thus fixed between the connection plates. The connection plates are at the same time radially centered by means of the intermediate element. The radial centering of the connection plates is essential for exact coaxial alignment of the drive shafts of the hydraulic pumps.
The intermediate element can be formed, for example, in a simple manner as a discoid cylindrical body. In this case the recesses in the connection plates are also cylindrical and their diameter corresponds to that of the intermediate element. The two connection plates and thus the two drive shafts are therefore exactly centered by inserting the intermediate element in the recesses in the connection plate. This formation of the intermediate clement entails an extremely low cost and is suitable for hydraulic pump units in which the hydraulic pumps only have to be mechanically and hydraulically connected together, without a booster pump having to be integrated into the connecting piece.
The connection plates can be screwed together in a radially outer region. The intermediate element can comprise at least one ring channel, so that different arrangements of the individual ports are possible.
A booster pump in the form of a gear pump, for example, can be integrated into the intermediate piece. The intermediate element is then divided into a main body and an insert body, which is inserted in a recess in the main body and holds the booster pump. The main body forms a first axial projection and the insert body a second axial projection, each of which projections engage in a recess in the two connection plates. The overall result of this is likewise centering of the two connection plates by means of their recesses and the intermediate element disposed in between. It is in this respect also advantageous here if the recesses in the connection plate and the main body are cylindrical and have the same diameter. A low-pressure port and a connection from the booster pump to a first ring channel, which adjoins the connection plates, is integrated into the main body. A connection from the booster pump to a second ring channel, which adjoins the other connection plate, is integrated into the insert body. The ring channels guarantee a flexible connection to the low-pressure ports in the respective adjoining connection plates. The connection plates and the main body can then be screwed together in a region radially surrounding the insert body.